Lung Abscess - ICUNOTES

🫁 Lung Abscess

🔍 Definition:

A lung abscess is a localized area of necrosis of pulmonary parenchyma forming a cavity containing pus, usually due to infection.

It is a type of necrotizing pneumonia, most commonly due to aspiration of oropharyngeal contents.

Classification:

Type	Features
Primary	Direct result of infection (usually aspiration); accounts for 80% cases
Secondary	Due to obstruction (tumor, foreign body), hematogenous spread, or immunosuppression

🧪 Etiology:

🦠 Common Pathogens:

Organism Type	Examples
Anaerobes (common)	Bacteroides, Fusobacterium, Peptostreptococcus
Aerobes	Staphylococcus aureus, Klebsiella pneumoniae, E. coli
Mixed flora	Especially in aspiration
Fungal (immunocompromised)	Aspergillus, Nocardia, Histoplasma
Tubercular abscess	Can mimic lung abscess

Anaerobes are the most common cause, especially after aspiration.

Pathophysiology:

Most common location: Posterior segment of right upper lobe or superior segment of right lower lobe(gravity-dependent zones in recumbency)

Risk Factors:

🧬 Clinical Features:

Symptom	Description
Fever, chills	May be high-grade
Productive cough	Foul-smelling purulent or bloody sputum
Night sweats	Especially in chronic cases
Pleuritic chest pain	Due to pleural involvement
Hemoptysis	From erosion into blood vessels
Weight loss	In prolonged illness
Clubbing	In chronic cases

🧪 Investigations:

🩻 Imaging:

Modality	Findings
Chest X-ray	Thick-walled cavity with air-fluid level (usually >2 cm)
CT Thorax	More sensitive; detects smaller abscesses, adjacent consolidation, rule out malignancy

CT is crucial to differentiate from necrotic tumors, cysts, or fungal cavities.

🧫 Microbiological Tests:

Sputum Gram stain and culture (limited utility due to oral flora contamination)
Bronchoscopy with protected brush or BAL for accurate sampling
Blood cultures (may be positive in severe or septicemia)
Serologies in atypical infections (TB, fungi)

🧪 Differential Diagnosis:

Condition	Key Differentiator
Necrotic tumor	Irregular margins, older age, no fever
TB cavity	Upper lobe predilection, systemic symptoms, night sweats
Hydatid cyst	History of exposure, water lily sign
Fungal abscess	Immunocompromised, halo or air crescent signs
Bronchiectasis	Cylindrical or saccular dilatation, no single cavity

Management:

A. Medical Management (First-line)

Strategy	Details
Empirical antibiotics	Clindamycin (600–900 mg IV q8h) or Ampicillin-sulbactam or Carbapenems
Duration	4–6 weeks IV, may step down to oral (clindamycin, amoxicillin-clavulanate)
Supportive care	Oxygen, hydration, chest physiotherapy, nutrition

🔬 Antibiotic Choices:

Setting	Likely Organisms	Empiric Therapy
Community-acquired	Anaerobes, streptococci	Clindamycin or beta-lactam + beta-lactamase inhibitor
Hospital-acquired	MRSA, GNBs, Pseudomonas	Vancomycin + Piperacillin-tazobactam or Meropenem

B. Indications for Drainage or Surgery:

Procedure	Indications
Percutaneous drainage	Large abscess (>6–8 cm), non-response to antibiotics, impending rupture
Surgical resection	Massive hemoptysis, bronchopleural fistula, failed medical therapy, underlying malignancy

⚠️ Complications:

🧾 Prognosis: